This invention relates to security devices bearing holographic images, of the type commonly applied to personal identification cards, various types of documents or other substrates, and to methods of making such devices.
As described for example in U.S. Pat. Nos. 5,145,212 and 4,913,504, to protect a credit card or other article or document of value against counterfeiting, a label or like device bearing a relief holographic image may be applied thereto. Holographic images are inherently extremely difficult to replicate effectively; moreover, in the described security device, the relief image is cast on a surface facing the substrate, so as to be inaccessible for taking impressions. Owing to this combination of characteristics, devices of the type described have won very wide acceptance.
Notwithstanding the success of such known holographic image-bearing security devices, it would be desirable to provide enhanced or additional security features in these devices, and to do so in a simple and economical manner, preferably capable of implementation with a minimum of modification in existing types of production lines.
An object of the present invention is to provide holographic image-bearing security devices, e.g. labels, for application to cards, documents and/or other substrates, characterized by a new and improved feature for making attempted tampering evident. Another object is to provide tamper evident security labels or overlaminates which combine both a readily verifiable overt security feature through the use of a holographic image and a covert security feature through the use of an invisible pattern that only becomes evident upon an attempt to delaminate the device from the surface to which it is adhered.
A further object is to provide a relatively simple and cost effective method of making tamper evident security devices of the type bearing holographic images. A still further object is to provide such a method of mass producing tamper evident holographic security products by radiation casting techniques.
To these and other ends, the present invention in a first aspect broadly contemplates the provision of a security tamper evident holographic label or like device affixable to a substrate such as a card, document or other article. The security device of the invention comprises a clear protective layer having opposed surfaces; a thin patterned layer of a clear resin cast onto a surface of the protective layer in a pattern such that some portions of that protective layer surface are covered, and other portions are not covered, by the patterned layer; a holographic image layer of a resin bearing a holographic image and having opposed surfaces of which one faces toward, and is bonded to, the patterned layer and portions of the protective layer surface that are not covered by the patterned layer, the bond of the image layer to the not-covered portions of the protective layer surface being stronger than the bond of the image layer to the patterned layer; a reflective layer strongly attached to the image layer; and an adhesive layer, bonded to the reflective layer, for affixing the device to a substrate.
This article, when adhered to a identification card or other base substrate by the adhesive layer, will exhibit no discernible security feature to the unaided eye owing to the thinness of the clear security patterned layer. If delamination of the article is attempted, however, the holographic image layer will be broken at the weakest interfacial bond, which is between the patterned layer and image layer surfaces, making evidence of tampering visible in the form of a break pattern identical to that of the clear patterned layer.
As an important particular feature of the invention, for achieving the foregoing and other advantages, both the patterned layer and the holographic image layer of the device are constituted of ultraviolet cured resin. The patterned layer and the image layer can be made of the same type of ultraviolet cured resin, or can be made of exactly the same resin.
In a second aspect, the invention contemplates the provision of a method for making a security device as described above, including the steps of providing a clear protective layer having opposed surfaces; radiation casting, on one of the surfaces of the protective layer, a thin patterned layer of a clear radiation curable resin, the patterned layer being cast onto the protective layer in a pattern such that some portions of the protective layer are covered, and other portions are not covered, by the patterned layer; radiation casting a second layer of a clear radiation curable resin bearing a holographic image onto the patterned layer and portions of the protective layer that are not covered by the patterned layer, the materials of the protective layer, patterned layer and second radiation curable resin layer being such that the last-mentioned layer bonds more strongly to the not-covered portions of the protective layer surface than to the patterned layer; strongly attaching a reflective layer to the last-mentioned image layer; and bonding an adhesive layer to the reflective layer, for affixing the device to a substrate. The protective layer and the patterned layer are subjected to a corona treatment before the holographic image layer is cast thereover.
Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawing.